This invention generally relates to the field of superconducting ceramics and particularly to manufacturing methods for making superconducting ceramics under a magnetic field.
It has long been known that metals such as mercury and lead, intermetallics such as NbNd, Nb.sub.3 Ge and NbGa and ternary materials such as Nb.sub.3 (Al.sub.0.8 Ge.sub.0.2) demonstrates superconductivity. However, the transition temperature of such long known conventional superconducting materials cannot exceed 25.degree. K.
In more recent years, superconducting ceramics have attracted widespread interest. A new material was first reported by researchers at the Zurich laboratory of IBM Corp. as Ba--La--Cu--O-type high temperature superconducting oxides. Subsequently, La--Sr--Cu(II)-O-type superconducting oxides were also proposed. Another type of superconducting material that has been found is (YBa.sub.2)Cu.sub.3 O.sub.6-8. By virtue of the fact that these superconducting ceramics form a quasi-molecular atomic unit in a crystalline structure whose unit cell is constructed with one layer in which electrons have essentially one-dimensional motion, whereas three dimensional electron condition occurs in the long known materials mentioned above, higher transition temperatures were achieved.
Much work has been undertaken by researchers in the field who have endeavoured to elevate Tco, the temperature at which resistance vanishes, above the levels previously obtained and preferably above the boiling point of nitrogen (77.degree. K) or even higher. As described in our European Patent Application No.87309081.5, we have investigated superconducting ceramic materials having the stoichiometric formulae (A.sub.1-x B.sub.x).sub.y Cu.sub.z O.sub.w, where A represents one or more elements of Group IIIa of the Periodic Table, e.g., the rare earth elements, and B represents one or more elements of Group IIa of the Periodic Table, e.g. the alkaline earth elements including beryillium and magnesium, and in the continuation of these investigations we have disclosed that the existence of voids and grain boundaries in superconducting ceramic materials makes it difficult to obtain an elevated Tco.